Oily film can be a number of things but if the inside of your tanks are red and you're seeing the oily film I'd suspect iron bacteria. It tends to get worse on the hot side, as they thrive in the heater.

I have no idea what a "whole house ph system" is.

You'll need to have the water sampled and checked for contaminants. Usually the only ones they check for now are coliform, nitrate, and arsenic, unless you have requested a specific test and usually you will need to pay for this out of your own pocket anyway.

Sounds like your iron bacteria problem if that's what it is, isn't horrible. High presence of iron bacteria usually will show up in your toilet tanks too.

This is all just speculation on my part. You really should have the water checked out by someone who specializes in water treatment systems.

Iron bacteria is generally not a health issue. Iron bacteria can be reliably diagnosed by orange staining and slime on the walls of the toilet tank. Perhaps what you are describing as oily is slime?

A very reliable method to get rid of iron and iron bacteria is to use chlorine (bleach) injection followed by a retention tank (typically 120 gallons) to allow contact time, followed by a backwashing granular activiated carbon filter (GAC) of the appropriate size for the design water flow of your treatment system. Most of the iron and iron bacteria will preciptate out in the retention tank and are periodically drained off the bottom of the tank. Any remaining particulate matter and any excess chlorine are removed by the carbon filter. Ongoing expense is for household bleach as the chlorine source (very inexpensive) and periodic replacement (rebedding) of the carbon media. Frequency of rebedding depends on water usage, how well you monitor and control excess chlorine, and the volume of the carbon.

Periodic maintenance (weekly is best) includes regular monitoring of residual chlorine in the water after the retention tank and before the carbon filter, adjustment of the chlorine injection as needed based on residual chlorine, and checking the level of the chlorine storage container and adding as necessary. The carbon bed typically lasts a few years before rebedding.